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Referees question No.1From: CommentsList of Questions (1) Calorimeters and Tracking, technical issues Trigger/DAQ, RICH and Physics related questions will follow. Tatsuya =============================================== Calorimeters by Antonio Ereditato I personally concentrated on the sessions about calorimetry and I wish to make comments on this subject and ask some questions to better understand the principle of the design and the motivation of specific technical choices. The main point concerns the overall design of the calorimeter system. It seems to me that some attention may still be paid to its optimization by stressing that the three calorimeters (preshower, ECAL and HCAL) must act as parts of a whole system. This could bring to better performance without (or with limited) additional investments. As a practical example, to trigger the discussion on this subject, one could envisage a design like the following one: 1) reduce the instrumented depth of HCAL (to 3-4 lambda?). Keep the same iron thickness for muon filtering. 2) Increase the longitudinal readout segmentation for ECAL (e.g. by suitable fibre grouping). One could foresee readout at 1 X0, at shower maximum (where the highest dose is released) and at shower tail. 3) The above design does not foresee a separated preshower, whose task would be accomplished by the first longitudinal readout sector of ECAL (at 1 X0). However, the type of photodetector could be different for different sectors. 4) Pointing or quasi-pointing geometry for ECAL and (possibly) HCAL can be envisaged. The gain in the performance must then be evaluated costwise.
A first set of additional questions (of lesser relevance) are listed below: i) HCAL is not compensating. This implies e>>p and a (trigger-) bias could appear in the pt measurement, given the energy dependence of the e.m. content of hadronic showers. ii) Pizero reconstruction capability is an important issue for a dedicated experiment like LHCb. How is the calorimeter design optimized for the pizero detection ? (e.g. module x-section, geometry, longitudinal segmentation,..) iii) How good and how critical is the calorimeter(s) hermeticity, given the constraints of a realistic engineering design ? iv) What is the scheme to cross-calibrate different calorimeters and different sectors ? v) Will fibers in ECAL and HCAL be aluminized at one end ? vi) It seems that no light mixers are foreseen between fibers and photodetectors. This may introduce systematic effects due to disuniformities in the response at the photodetector surfaces (boundary effects). =============================================== Tracking by Andrey Rostovtsev ----------------------------------------------- Vertex Detector: - Alignment precision required for vertex trigger is less than 6 micron. This has to be redone online at least after each retraction. Do you have an estimate, how long does it take to obtain the new alignment constants for the trigger? - Could you explain the numbers for the efficiency in three different radiation dose scenarios given on p.46? - In case the aperture for stable LHC beam will turn out to be more than project value(1mm), how big is a clearance the vertex detector can still allow without a substantial deterioration of the detector performance? ------------------------------------------------ Main Tracking: - Have you studied a scenario with two--dimensional readout? - Given a close similarity of LHC-b and HERA-b tracking detectors could you explain an origin of much better mass resolution in LHC-b detector (15MeV in LHC-b vs. 23 MeV in HERA-b for B-->pi+pi-). - What is an effective thickness of one outer tracker station? - When do you plan to have a prototype of outer tracker station for the beam tests this year? ------------------------------------------------ Muon Tracking - The requirement 5 out of 5 stations in the muon trigger implies very high efficiency and reliability of the system. Assuming a risk to operate in condition 4 out of 5 stations, could you quantify a deterioration of the performance of the muon detector? - Could you quantify a misidentification probability you expect in the muon system? The number for hadrons firing only 0.2% of the total trigger rates (p.108) says that you have very clean muons already at trigger level with quite modest Pt requirement. - What is P_t resolution of the muon system? - If i read fig 11.2 for M1 the occupancy is expected to be below 2-3 % at any radius in M1. Is it correct?
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